CHICAGO — Strengthening the hip abductor muscle may delay progression of medial compartment knee osteoarthritis, according to findings reported at the 2004 World Congress on Osteoarthritis.
The study showed that a greater internal hip abduction moment—or torque generated by the body during walking— protected against medial tibiofemoral osteoarthritis (OA) progression in the ensuing 18 months in patients with knee OA.
Frontal knee mechanics have received most of the attention in knee OA studies. But such studies don't address the issue of stability since few knee muscles specifically provide frontal plane stability, said Alison Chang, a physical therapist at Northwestern University, Chicago.
Instead, hip frontal plane muscles may play a key role in regulating knee load and providing such stability. In addition, “hip muscles have greater cross-sectional area, and can probably generate greater forces or torques,” Ms. Chang explained at the congress, sponsored by the Osteoarthritis Research Society International.
The investigators hypothesized that a decrease in hip abductor muscle torque during walking would lead to an increase in medial tibiofemoral joint loading, and thereby to medial OA progression.
The idea is that during level walking the hip abductor muscles of the stance leg contract to control the slight lowering of the contralateral pelvis. Weakness of the hip abductor muscles in the stance leg may cause an additional drop in the contralateral swing leg. Such a drop would shift the body's center of gravity toward the swing limb, thereby increasing forces across the medial tibiofemoral compartment cartilage of the stance knee, and potentially increasing OA progression.
In the study, conducted in collaboration with Rush University Medical Center in Chicago, 64 patients with mild to moderate OA were evaluated using a motion-capturing system to determine kinematics and kinetic gait parameters at baseline and at 18 months. Inverse dynamics were used to calculate three-dimensional moments at the hip, knee, and ankle joints.
Pain was evaluated using a visual analog scale for each knee. Disease progression was defined as worsening of medial joint space narrowing.
The mean peak internal hip moment was calculated by finding the peak internal hip abduction moments during several gait cycles for each individual and then computing the mean. From these figures, the investigators were able to estimate peak hip abductor muscles activity during the gait cycle.
The mean age of the patients was 66 years, 63% were women, mean body mass index (BMI) was 29, and the mean peak internal hip abduction moment was 4.19% of body weight multiplied by height.
Logistic regression analysis showed that a greater internal hip abduction moment during walking was significantly associated with a reduced likelihood of medial tibiofemoral OA progression at 18 months (odds ratio of 0.63).
This strong protective effect remained after adjustment for age, gender, gait speed, physical activity level, knee pain severity, and knee OA severity (OR 0.52). Further adjustment for ipsilateral hip OA and hip symptoms did not change the odds ratio.
The odds of OA progression were reduced by 50% per additional unit of internal hip abduction moment.
“The results suggest the need for interventional strategies to increase internal hip abduction moments such as hip abductor muscle strengthening in both static and dynamic positions,” Ms. Chang said.